1. Field
The present invention relates to improvement of airbag devices for saddle-ride type vehicles.
2. Description of the Related Art
Known airbag devices for saddle-ride type vehicles include an acceleration sensor for an airbag device for motorcycles provided near the tip of the front fork (see for instance JP Patent No. 4052531 (Japan '531) and JP-A-No. 2007-69699 (Japan '699).
According to FIG. 3 and FIG. 5 of Japan '531, a front fork to support a front wheel is disposed in the front part of the body, and a sensor for detecting acceleration in vehicle collision is provided near the tip of this front fork. In more detail, the sensor is arranged within the axle for the front wheel disposed in the front fork.
By disposing the sensor near the tip of the front fork in this way, it is made possible to detect acceleration at the time of vehicle collision immediately.
According to the known embodiment described above, an impact detecting sensor is positioned within an axle cylinder and, moreover, above the center of the body. As it is thus positioned near the steering axis line of the front fork, in frontal collision the impact transmitted from the front wheel via the axle can be sensitively detected while the steering components are removed.
Meanwhile, an airbag device requires a mechanical safetying sensor or interlock or an electronic safety system, intended to prevent the airbag from being deployed by an erroneous action of the sensor or the microcomputer that generates an airbag driving signal.
According to FIG. 3, FIG. 4 and FIG. 5 of Japan '699, left and right front forks to support a front wheel are disposed in the front part of the body, and main sensors for detecting acceleration at the time vehicle collision are provided on these front forks. Furthermore, a sub-sensor is provided integrally with the left and right front forks above the main sensor or the main sensor or behind a cross member laid between the left and right front forks.
It is intended to prevent the airbag from being erroneously deployed by any faulty operation of a single sensor by subjecting output signals of the main sensor and the sub-sensor to collision determination by an operation control section in accordance with the flow chart of FIG. 10 of Japan '699.
According to this known case, since the impact detecting main sensor is positioned on each of the left and right front forks, and their signals are averaged for use in collision determination, in frontal collision the impact transmitted from the front wheel via the axle can be sensitively detected while the steering components are removed.
Moreover, as the sub-sensor 12 is similarly positioned on the front forks 1 or the cross member 40, unless both the main sensor 11 and the sub-sensor 12 positively determine collision, no deployment signal is issued to the airbag. Thus, it is intended to prevent the airbag from being erroneously deployed even if either sensor fails to function and an ON determination is made.
According to Japan '531, as the sensor is disposed within the axle and its shape is determined by the external diameter of the axle among other factors, it becomes a dedicated component of the pertinent vehicle and is expensive.
According to Japan '699, the main sensor and the sub-sensor are arranged on the front forks where the available fitting space is reduced by the fitting of a brake caliper and a front fender among others, the freedom of arrangement is restricted. Moreover, one main sensor on each of the left and right sides and one sub-sensor on each of the left and right sides or one on the cross member are required, so that at least three sensors are needed and the number of parts is large, resulting in an increase in cost.
Besides, as the sensor and a collision judging unit disposed on the body side are distant from each other, the overall length of a harness connecting these sensor and collision judging unit 16 is extended. Moreover, as there is significant bending or flexing when the handlebar is steered, an expensive harness that can withstand significant bending or flexing.
Furthermore, though the sensor fitted to the front fork, when the vehicle has collided, can immediately detect the collision of the front wheel for instance, detection of acceleration in the longitudinal direction when the front wheel has ridden over a level gap during normal running for example, and consideration should be given to preventing this detection from affecting the operation of the airbag.